3
votes
1answer
452 views

Is no caching mode page a serious error?

My server log displays the following error messages in RED: kernel: sda: sda1 sda2 kernel: sd 0:1:0:0: [sda] No Caching mode page found kernel: sd 0:1:0:0: [sda] Assuming drive cache: write through ...
5
votes
1answer
181 views

How to use an SSD for caching, so my hard disks can spin down?

I've got a file server with a bunch of disks running together in a BTRFS pool and want to add an SSD for caching. I'm not mainly after speeding up things, but want to catch the regular small accesses ...
3
votes
1answer
660 views

Measure hard-disk read(), write() speed without caching in QNX 6.5

I am working on QNX 6.5 Operating system. QNX 6.5 supports POSIX APIs. I am trying to build an application which is used to evaluate performance of hard-disks. My application will read/write/read ...
4
votes
4answers
447 views

If I have an SSD and a hard disk in a system, can the SSD act as cache for the hard disk?

Say I have some partitions; one on a SATA drive and one on an SSD. I want to create a "virtual" hybrid disk. Is this possible?
13
votes
1answer
2k views

Is disabling barriers for ext4 safe on a laptop with battery?

The manual page says about the barrier option for ext4: Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance ...
7
votes
2answers
1k views

How to time grep commands accurately?

I want to compare the speed of these two commands: grep pattern1 files* grep pattern2 files* Unfortunately, the first grep reads much of files* into memory buffers, so the second grep runs ...
5
votes
1answer
374 views

Why doesn't dm-crypt handle write barriers properly?

One of the well-known properties of dm-crypt is that it does not handle write barriers properly and hence it requires turning off on-drive write cache to prevent corruption of filesystems. As far as I ...